The present invention relates to cam-operated timers for appliances.
Many household appliances are equipped with mechanical timers to control their operation. Examples include dishwashers, icemakers, clotheswashers and dryers, wall and outlet timers, microwave ovens, and various other appliances.
While there is thus a diverse variety of applications for timers, most timers have a similar general structure. Typically, the timer includes a wheel or drum outfitted with cam surfaces. Spring metal switch arms are mounted to ride on these cam surfaces to be raised and lowered from the wheel or drum surface in response to the elevation of the cam surfaces.
A timing motor is typically coupled to rotate the cam wheel or drum, such that the switch arms are raised or lowered in accordance with a predefined regular pattern that is defined by the elevation of the cam surfaces on the wheel or drum. In some timers, the timing motor moves the wheel or drum by causing drive pawls to oscillate and move the cam wheel or drum forward in a step-by-step fashion. In other timers, the timing motor is connected through a gear train to a toothed surface on the cam wheel or drum to rotate the cam wheel or drum in a continuous manner. In either case, the timing motor and its stator, rotor and windings is typically a separately assembled part, housed in a separate housing from the drive assembly; as a consequence, the combination of the timing motor and gear train are fairly substantial in size, and form a large part of the volume and weight of the timer.
The switch arms inside the timer are typically mounted in pairs such that cam-actuated motion of either or both switch arms of a pair causes the pair of arms to make or break and electrical contact therebetween. The switch arms thus form an electrical switch that controls the operation of the appliance. In some timers, switch arms are mounted in groups of three so as to form a single pole, double throw switch or other more complex switching arrangement.
The contacting surfaces of the arms are often coated with expensive metals such as silver alloy to facilitate good contact between the arms and minimize the effects of corrosion. To further facilitate contact between the arms, in some timers a contact rivet is included on each arm, extending toward the opposite arm, such that contact is made between the rivets on the switch arms. To avoid the cost of making and assembling this additional contact rivet, in other timers the arms are stamped with a xe2x80x9cdimplexe2x80x9d, i.e., a raised section of metal that extends toward the opposite arm to form a contact surface. This approach is useful in containing costs where it can be applied; however, where the switch arms are mounted in a group of three, the central switch arm cannot be dimpled to form a contact, since the dimple can only extend in one direction relative to the surface of the central switch arm and the central switch arm must make contact with the arms above and below it. Accordingly, when three switch arms are stacked in this manner, the central switch arm must be outfitted with a contact rivet in order to have surfaces that extend toward both neighboring arms, increasing costs.
In a typical timer there are multiple switches and thus multiple groups of two or more switch arms that interact with the cam surfaces on the cam wheel or drum. In such timers, often the switch arms are mounted in xe2x80x9cwafersxe2x80x9d; that is, the respective upper arms of each switch is mounted in a first wafer, and the respective lower switch arms of each switch is mounted in a second wafer. The wafers are typically formed of plastic molded over the ends of the switch arms opposite their cam-actuated surfaces. To mount the switch arms for actuation by the cams of the wheel or drum, the wafers are stacked atop each other, and affixed to the timer housing, so that the arms are suspended in a specific position relative to the wheel or drum of the timer.
To assure proper switch functions, the position of the switch arms relative to the wheel or drum, must be controlled to fairly tight tolerances. This means that the size of the wafers, and the position of the switch arms in the wafers, and the mountings to which the switch wafers are mounted, must also be controlled to tight tolerances. Unfortunately, where two or three wafers are stacked to create switch groups of two or three arms, the necessary tolerances become difficult to satisfy, most particularly because it is difficult to maintain a tight tolerance in the switch mounting surfaces that span a long distance, e.g., the entire height of a stack of three wafers. Manufacturing wafers and mountings to sufficiently tight tolerances is thus difficult and expensive.
The switch arms in a wafer are typically made of the same material. Inexpensive metals such as alloy brass are typically used to make switch arms for low current applications. In higher current applications, more expensive, more highly conductive metals such as copper alloy are used to minimize resistance and the resultant heat and energy loss. Unfortunately, even if only one pair of switch arms carries high current, the need for more expensive metals in the switch arms substantially increases the cost of the timer.
The appliance operator typically sets the timer using a knob that extends outside of the timer housing and can be grasped by the operator. In a typical clotheswasher timer, for example, the operator rotates the knob in a forward direction, thereby rotating the cam wheel or drum in a forward direction, until the cam wheel or drum is an appropriate initial position to begin a timed operation cycle. The user then presses a button, or moves the knob axially to initiate the cycle and also start the timing motor.
As is familiar to most users of household appliances, a substantial clatter is generated by the interaction of the cam-operated switches and drive pawls and/or any one-way or ratchet clutch when the timer is advanced to the appropriate position to begin a cycle. For example, the drive pawls click across the pawl-driven surfaces of the cam wheel or drum as the wheel or drum is advanced, and at the same time, the cam operated switch arms click as they are opened and closed by the cam surfaces as the wheel or drum is rotated, and any one-way clutch also clicks. The resulting noise is unpleasant, and is accompanied by substantial irregular tactile feedback.
A second difficulty is that the timer must be set by rotation in a single direction. This constraint arises from the fact that the cam surfaces on the drum or wheel typically are formed with sharp drop-offs so that switches are closed or opened rapidly. Reverse rotation of the cam will cause the cam surfaces on the drum or wheel to bind against the switch arms, preventing further reverse rotation and potentially damaging the timer. To prevent damage by reverse rotation timers often include a rachet pawl or other mechanism to block reverse rotation; of course, this structure only enhances the clatter generated during forward rotation of the timer for setting.
Recently, so-called xe2x80x9cquiet setxe2x80x9d drum-type timers have been introduced. In these timers, a mechanism lifts the switch arms and drive pawls from the surface the drum to disengage the drum from the pawls during setting. This permits the drum to be rotated manually without clatter from the pawls and switch arms, and also permits bi-directional rotation during setting because the pawls and arms are disengaged from the drum surface.
Unfortunately, users have become accustomed to receiving tactile feedback when setting a timer, and may prefer to receive such feedback. A xe2x80x9cquiet setxe2x80x9d timer, therefore, may be perceived as undesirable as compared to a timer that does provide tactile and audible feedback such as a prior non-xe2x80x9cquiet setxe2x80x9d timer.
In accordance with the present invention, the drawbacks and difficulties with known cam-operated timers are overcome.
In a first aspect, the invention features a cam-operated timer having a setting feedback function. The timer includes an audible and/or tactile feedback member that is not part of the drive mechanism nor part of the cam-actuated switches of the timer (but may include parts of the cam-carrying member). The audible and/or tactile feedback member is positioned within the timer to engage a textured surface that rotates with or in response to rotation of the timer""s cam-carrying member (e.g., the timer""s cam wheel or drum), so that upon rotation of the cam-carrying member, the audible and/or tactile feedback member produces desired audible and/or tactile feedback.
In the disclosed specific embodiment, the audible and/or tactile feedback member is a shaped spring member, e.g., a xe2x80x9cVxe2x80x9d-shaped or xe2x80x9cUxe2x80x9d-shaped member, which engages to a textured surface comprising a series of ridges or teeth. The textured surface may be carried on the cam-carrying member itself, and the audible and/or tactile feedback member is mounted to the housing so as to engage the textured surface of the cam-carrying member at all times. In other contemplated embodiments, the audible and/or tactile feedback member may be engaged to other members that rotate with the cam-carrying member, rather than to the cam-carrying member itself. Furthermore, the audible and/or tactile feedback member need not always engage to the associated textured surface, but may only engage the associated textured surface when an operator places the timer in a manual setting mode (by, e.g., axially displacing a shaft that serves as the axis of rotation for the cam-carrying member).
In the disclosed specific embodiment, the timer further includes an actuator for engaging the cam-actuated switches and moving the cam-actuated switches away from the cam surfaces of the cam-carrying member when the operator places the timer in a manual setting mode. Further, a clutch is included in the drive mechanism for permitting slip in the drive train between the timing motor and cam-carrying member when the operator places the timer in a manual setting mode. When these elements are utilized, the sole source of audible and/or tactile feedback to the operator when manually setting the timer is the audible and/or tactile feedback member, so that the xe2x80x9cfeelxe2x80x9d of the timer during setting can be tightly controlled and customized. In particular, different models of an appliance line can be distinguished by the audible and/or tactile feel provided by the timer during manual setting. A timer used in the top of the line appliance model can be provided with a feel that is found to be most desirable to typical customers. Gradations of feel can be provided to different timers on lower end models.
The textured surface of the cam-carrying member, and the surface of the audible and/or tactile feedback member that engages to the textured surface, can be configured in various ways to provide the desired audible and/or tactile feedback. Specifically, the ridges on the textured surface and on the engaging surface of the audible and/or tactile feedback member can be made relatively smooth and rounded, or relatively sharp-edged, to change the audible and/or tactile feedback. Furthermore, the spacing between the ridges or teeth on the audible and/or tactile feedback member can be made wider or narrower, regular or irregular, intermittent or random, to change the audible and/or tactile feedback.
Another aspect of the invention relates to the clutch included in the drive mechanism. As noted above, the clutch permits slip in the drive train between the timing motor and cam-carrying member when the operator places the timer in a manual setting mode. When the timer is in its run mode, the clutch also permits forward rotation of the cam-carrying member independently of the timing motor, but prevents independent reverse rotation of the cam-carrying member.
In the disclosed embodiment, the clutch is in the form of a first rotating member and a second rotating member that are included in the drive train between the timing motor and cam-carrying member. The first and second rotating members each include a plurality of protrusions about their surface. When the first and second rotating members are axially aligned, the protrusions of the first rotating member mesh with the protrusions of the second rotating member so as to engage the second rotating member and force reverse rotation of the second rotating member upon reverse rotation of the first rotating member, but permit slip between the second rotating member and first rotating member upon forward rotation of the first rotating member. When the first and second rotating members are not axially aligned, there is no engagement between the protrusions of the first and second rotating members.
In the specific embodiment that is disclosed, the first and second rotating members are gears in the drive train between the timing motor and cam-carrying member. The first rotating member has a plurality of clutch teeth positioned about an inside periphery thereof, and the second rotating member has a plurality of clutch prongs sized to engage the clutch teeth. The first rotating member is annular and defines an orifice about its axis of symmetry. The second rotating member is placed through the orifice so that the clutch prongs of the second rotating member can be axially aligned with the clutch teeth of the first rotating member.
The clutch prongs are circumferentially spaced so that the prongs do not simultaneously align with the clutch teeth. Specifically, there are m prongs circumferentially spaced about the second rotating member, and n teeth circumferentially spaced about the first rotating member; the prongs and teeth are arranged such that exactly one prong aligns with exactly one tooth every 360/mxc2x7n degrees of relative rotation of the first and second rotating members. In the disclosed specific embodiment, there are five prongs (m=5) and twenty-four teeth (n=24), so that a prong aligns with a tooth every three degrees of relative rotation of the first and second rotating members. Furthermore, the prongs are spaced so that, from a position where a prong on the second rotating member is aligned with a tooth on the first rotating member, three degrees of relative rotation will bring a prong on approximately the opposite side of the second rotating member into alignment with a tooth on the first rotating member.
A third aspect of the present invention relates to structures of the switch arms in the timer. Specifically, the contacting surfaces of one or several switch arms are lanced, that is, there is a tear in the surface of the switch arm, and adjacent the tear a first portion of the contact surface of the arm is deflected away from the surface of the switch arm in a first direction. This structure provides a sharp contact edge that permits the switch arm to make good contact with adjacent switch arm(s) while reducing the effects of corrosion, without resorting to the use of expensive contact metal coatings.
In the illustrated specific embodiment of the invention, a second portion of the contact surface adjacent to the tear in the switch arm, extends away from the surface of the switch arm in a second direction opposite to the first direction. Thus, there are two lanced portions in the contact area of the switch arm extending in opposite directions, so that a switch arm mounted between two other switch arms will have extending portions suitable for making contact with both other switch arms.
A fourth aspect of the present invention relates to the mounting of the switch arms to the timer housing. The housing includes first and second locating areas for receiving first and second switch arm wafers. A first switch arm wafer is mounted to the housing and rests against the first locating area, and a second switch arm wafer is stacked atop the first switch arm wafer and rests against the second locating area. In this manner, the variation in the position of each switch arm wafer is reduced. The effect of inaccuracies in the molding of the wafer or of the housing can be minimized since each switch arm wafer is separately located within the housing.
In the disclosed specific embodiment of this aspect, the first and second locating areas comprise first and second steps, and the first and second switch arm wafers are sized such that the first switch wafer fits to the first step and inside of the second step, and the second switch arm wafer fits to the second step and overlaps the first. In addition, the first and second locating areas comprise sections of one or more posts, each post having a first section with a first larger diameter and a second section with a second smaller diameter. The first switch wafer defines a locating hole with a diameter larger than the first diameter, and the second switch wafer defines a locating hole with a diameter smaller than the first diameter but larger than the second diameter, so that the first switch wafer fits over the first section of each post whereas the second switch wafer fits over the second section of each post. In embodiments with three or more switch wafers (such as is illustrated below), additional steps may be included to accurately locate those wafers as well.
In alternative embodiments, in place of steps, there may be a continuous ramp, such that the first switch wafer is sized to intersect the ramp in a first locating area, but the second switch wafer is sized to intersect the ramp in a second locating area. Furthermore, in place of stepped posts, there may be one or more continuously tapering posts, such that the first switch wafer""s locating hole causes the first switch wafer to engage the continuously tapering post in a first locating area, and the second switch wafer""s locating hole causes the second switch waver to engage the continuously tapering post in a second locating area.
A further aspect of the invention relates to the arrangement of switch arms in the wafers. Specifically, at least one of the switch arm wafers includes switch arms made of different metals. This allows high current and low current switches to be mixed in a single set of arms, where the high current switches are formed with wider and/or more expensive metal arms, and/or with a more heavy-duty contact, and the lower current arms are made with narrower and/or less expensive metal arms, and/or with a less heavy-duty contact.
An additional aspect of the invention relates to the arrangement of the geartrain and timing motor. The timing motor comprises a stator plate and a rotor mounted for rotation in the stator plate. The geartrain comprises meshing gears positioned on both opposite sides of the stator plate for providing a gear reduction of the rotation of the timing motor. By mounting the geartrain directly to the timing motor stator and including meshing gears on both opposite sides of the stator plate, the size of the timing motor and geartrain assembly can be substantially reduced as compared to prior systems in which the timing motor is contained within a separate housing and the geartrain is positioned entirely outside of this housing.
Another aspect of the timer of the present invention is the ability of the timer to provide a three-contact switch in which all three contacts may simultaneously be connected together. This capability can have useful application in some environments, and potentially reduce the number of switches that are needed.